As conventional art of this type, there is one disclosed in JP 11-082416 A.
According to this conventional technique, a hydraulic circuit system which is for arrangement, for example, in a hydraulic working machine is provided with at least one hydraulic pump, for example, two hydraulic pumps; plural actuators driven by hydraulic fluids delivered from these hydraulic pumps, for example, a right track motor, a left track motor, a swing motor, a boom cylinder, an arm cylinder and a bucket cylinder; plural flow control valves for feeding the hydraulic fluids, which have been delivered from the hydraulic pumps, respectively, to the above-mentioned plural actuators; a pilot hydraulic pressure source, and plural pilot operating units for producing operation signal pressures from the pilot hydraulic pressure source to change over the corresponding flow control valves.
The hydraulic circuit system also has shuttle valves for selecting maximum pressures of plural groups of operation signal pressures among the operation signal pressures produced by the above-mentioned plural pilot operating units; hydraulic selector valves arranged in association with the plural groups of operation signal pressures to operate based on the maximum pressures such that corresponding control signal pressures are produced from the pressure of the pilot hydraulic pressure and source and are outputted as pump control signals or the like; and a shuttle block with all of the above-mentioned shuttle valves and the above-mentioned hydraulic selector valves built therein.
The hydraulic circuit system is constructed such that it produces the above-mentioned control signal pressures in the shuttle block and by the control signal pressures, operates one or more operation devices arranged in association with any one or more of the hydraulic pumps, actuators and flow control valves, for example, one or more regulators for the hydraulic pump or pumps.
As the conventional technique constructed as described above is provided in the shuttle block with the plural shuttle valves and produces, produces in the shuttle block the control signal pressures for operating the operation devices, and outputs the control signal pressures, piping is no longer needed between the shuttle valves so that the construction of the circuit can be simplified. Accordingly, the hydraulic circuit system assures an improvement in assembly workability, can minimize losses upon transmission of signal pressures, and can operate control devices such as regulators with good responsibility.
With the above-described conventional technique, however, when the flow control characteristics of the regulators for the hydraulic pumps are determined in conformity with boom-raising operations, traveling operations and the like each of which requires a high pressure even when operated delicately, the delivery flow rate of the pumps increase even in a boom-raising operation or superstructure-swinging operation in which it is not desired to produce a pressure too much. As a consequence, the pressure becomes high, so that the operability of the boom-raising operation or superstructure-swinging operation is deteriorated to lead to a reduction in the accuracy of work performed by the hydraulic working machine. When the flow control characteristics of the regulators for the hydraulic pumps are conversely determined to produce a pressure at a suppressed level with a view to improving the operability of a boom-raising operation or superstructure-swinging operation, the operability of various operations which require high pressures such as boom-raising operations and traveling operations is deteriorated, resulting in a problem that the accuracy of various work performed by the hydraulic working machine is lowered.
The present invention has been completed in view of the reality of the above-described conventional technique, and has an object thereof the provision of a hydraulic circuit system for a hydraulic working machine, which can smoothly perform both of an operation requiring a high pressure and an operation which desires the production of a pressure at a suppressed level.